dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 19/04/11 19:21, Anders Logg wrote:
> Question #153459 on DOLFIN changed:
> https://answers.launchpad.net/dolfin/+question/153459
> 
>     Status: Open => Answered
> 
> Anders Logg proposed the following answer:
> On Tue, Apr 19, 2011 at 09:54:43AM -0700, Johan Hake wrote:
>> On Tuesday April 19 2011 09:45:58 Chaffra wrote:
>>> Question #153459 on DOLFIN changed:
>>> https://answers.launchpad.net/dolfin/+question/153459
>>>
>>> Chaffra gave more information on the question:
>>> The newton_solver is no longer accessible from VariationalProblem. I used
>>> to be able to set the linear_solver parameters via
>>> problem.newton_solver().linear_solver().parameters ... Is there a new way
>>> of doing this?
>>
>> I think Garth is the man to answer this, but I recall he removed that options
>> because it became difficult to maintain as the linear solver can be of many
>> different types.
>>
>> The solution, I think, is to create the linear solver before you create the
>> NewtonSolver, grab the parameters, create the NewtonSolver, change whatever
>> parameters to the LinearSolver you need through the grabed paraemters.
> 
> I think I made a change recently to include the Newton solver
> parameters in the parameter list for a VariationalProblem.
> 
> If you use
> 
>   info(problem.parameters, True)
> 
> then you should see the parameters for the Newton solver.
> 
> The solver type and preconditioner cannot be set by parameters at the
> moment. The problem is that the Newton solver gets these parameters in
> the constructor. It should use the parameter system instead.
> 

I don't think that it should use the parameter system. It complicates
the design (because objects can't be created in the constructor), and
it's not feasible to expose all solver and preconditioner parameters
from a VariationalProblem object.

The best approach to fine-grained control is to pass a linear solver
object to VariationalProblem at construction, and set parameters for the
solver object. NewtonSolver does this.

Garth


> --
> Anders
>